This invention relates to a dynamic vibration absorber for a hi-fi class phonograph tone arm.
Some phonographs of the hi-fi class have a tone arm provided with a dynamic vibration absorber comprising a mechanical resonance circuit with a mechanical yieldable element, for instance a steel spring and some weight means, for instance a part of a counterweight. The function of the dynamic vibration absorber is to reduce the lower resonance peak which results from the joint action of the effective weight of the tone arm and the yieldability of the stylus arm of the built-in stylus holder. A correct functioning of the dynamic vibration absorber is obtained if the major part of the counterweight yieldingly attached to the rear part of the tone arm behind the supporting bearing of the tone arm starts to oscillate at a frequency equal to the undesirable lower resonance peak. As a dynamic vibration absorber oscillates at a counter phase, its operation reduces the amplitude of undesirable oscillations and acts as an anti-resonator of the tone arm. The resistivity of the whole phonograph against shock disturbances in the sub-acoustic range is thereby also improved.
Actually known dynamic vibration absorbers have a major drawback in that they are unable to oscillate equally in all directions as would be required for optimum results with tubular tone arms because of a undesirable resonances of such arms in all directions. Another substantial drawback of known dynamic vibration absorbers is the circumstance that in order to secure the neccessary mechanical stability of the counterweight system, only part of the weight of the counterweight can be arranged yieldingly. The influence of a thus arranged dynamic vibration absorber for the reduction of the lower resonance peak is small since only a small part of the counterweight takes part in the oscillation, whereas in order to suppress the undesirable lower resonance, is desirable that the whole weight of the counterweight shall start to oscillate. Known dynamic vibration absorbers can only tenstively be tuned to the frequency of the lower resonance or tuned after repeated measuring, since there is no suitable aid or arrangement for making it possible directly to adjust the resonance frequency and the damping factor according to specifications from the manufacturer of the respective tone arm and of the built-in stylus holder. If the frequency and the damping are not correctly adjusted, the benefits obtained from the action of the dynamic vibration absorber are substantially reduced.